Flooring underlayments are conventionally applied to new construction or rehab work upon wood or concrete subfloors. Such underlayments are applied as a flowable slurry, and upon setting provide a level substrate that facilitates the application of finished flooring such as wood, tile, resilient flooring and carpet.
The industry standard underlayment is a Portland cement based material. However, gypsum based underlayments, such as LEVELROCK® gypsum underlayment (United States Gypsum Company, Chicago, Ill.) are gaining popularity. A conventional underlayment sealer is often utilized to seal the surface of a gypsum underlayment, but will not harden the surface in situations where unusual circumstances have caused softening of the top surface. Instead, the surface will be chalky, dusty or soft. These situations arise, for example, when a strong draft is present during the setting process, or when the wrong type or too much sand is utilized in the underlayment slurry mixture. Too much sand or the wrong type of sand will often cause addition of an excessive amount of water to achieve flow of the pourable underlayment slurry. A soft surface of a gypsum underlayment is undesirable, and also inhibits the formation of a strong bond with an elastomeric membrane directly applied or with an adhesive for installing a finishing flooring material.
Non-traditional elastomeric liquid coatings are becoming increasingly popular as waterproofing and crack isolation membranes for flooring systems. For example, MAPELASTIC® AQUA DEFENSE (Mapei Products for Building, Inc., Dalton, Ga.) waterproofing and crack isolation membrane is a well known elastomeric membrane. Such elastomeric membranes are coatings that are applied directly to an underlayment, and often take a considerable amount of time, sometimes several days, to develop a bond. The bond that does develop is not usually as strong as one would see with a traditional crack-isolation membrane. Elastomeric membranes are also applied to gypsum underlayments treated with a conventional sealer, creating a bond that is improved over the bond between the membrane and a bare gypsum underlayment surface. However, the bond still may not meet expectations of flooring contractors. Often times, it is possible to separate the elastomeric membrane from the underlayment with a simple knife and peel the coating off in sheets.
NORAMENT® and NORAPLAN® rubber flooring tile and sheet products, manufactured by Nora Systems, Inc. (Weinheim, Germany) are examples of commercially available specialty rubber floor finishing materials that are commonly used in hospitals, large building entryways, schools, and in other similar settings. The underlayment product of choice for hospital (or similar commercial building) renovations and new construction is LEVELROCK® 4500 NXG™, a gypsum-based underlayment manufactured by United States Gypsum Company. Because rubber floor tiles and sheets are not coatings, they are usually bonded to an underlayment with an adhesive, such as a polyurethane.
Conventionally, surface preparation of a LEVELROCK® gypsum underlayment for most traditional water-based adhesives is simply to make sure the surface is clean and dry. When utilizing rubber floor coverings, a polyurethane adhesive is conventionally employed. For example, NORA® 310 adhesive is a polyurethane adhesive recommended by Nora Systems, Inc. for installation of their resilient “rubber” floors. Although they work well with gypsum concrete underlayments, polyurethane adhesives are expensive, adding cost to a floor installation project. Manufacturers of high performance resilient floors also offer less expensive latex-based adhesives. Utilization of a water-based acrylic adhesive is, conventionally, insufficient. For example, NORA® 410 (water-based) adhesive, does not satisfactorily bond a rubber floor finish to a gypsum concrete underlayment, even when the contractor waits three days for the material to bond.
To address this problem, Nora Systems Inc., a manufacturer and installer of resilient rubber floors, recommends a “wet set” method of adhering a rubber floor to an underlayment that involves applying a water-based adhesive and allowing it to become tacky, but not completely dry, before installing the rubber floor. The “wet set” method, however, presents another problem. Any water remaining in the adhesive becomes trapped under the rubber floor, which is non-breathable. Eventually, this water seeps into the surface of the LEVELROCK® gypsum underlayment. As a result, the underlayment softens. In time, there is a failure of the bond between the underlayment and the rubber floor.
Along with the increasing popularity of gypsum based underlayments, elastomeric membranes and rubber flooring, there are problems related to bonding that are not prevalent with conventional cement-based underlayments and more traditional floor finishes.
The hygroscopic nature of gypsum floor underlayments may interfere with bonding between a water-based adhesive or an elastomeric membrane and a surface of a gypsum floor underlayment. Conventional solutions have involved utilization of an acrylic sealer applied to the surface of a dry underlayment. However, because the underlayment must be dry, the logistics and timing of application of these sealers becomes problematic. Conventional acrylic sealers will often trap water within the underlayment if the underlayment is not dry before applying the sealer. Problems associated with trapped water include easy peeling or delaminating of the sealer or other coatings applied to the underlayment.